Primarily due to their high energy density, lithium ion batteries (LIBs) are currently the commercially dominant energy storage devices, and extensive effort has been made to design nanostructured electrodes. However, as lithium precursor supplies are both limited and confined to narrow geographies, technology based on alternative charge carriers is being sought. Thus room-temperature sodium ion batteries (NIBs, NABs, SIBs) have gained increasing attention due to the wide availability and low cost of Na.
Substantial success has been recently achieved in developing cathode and anode materials for conventional sodium ion batteries. It is well established that graphite will not intercalate Na to an appreciable extent, due to its larger ionic radius than Li (0.102 nm vs. 0.076 nm) and weaker chemical interaction with the graphene sheets. There has been a range of alternative NIB anode materials published recently in literature, including nitrogen doped carbons, non-graphite carbon nanostructures, nanostructured red phosphorous, ionic compounds, nitrides, and metal oxides, as well as a range of Na active metal alloys with combinations of active and inactive phases. Graphene and graphene nanocomposites have also been utilized, along with Na intercalating “MXenes” where M is a transition metal and X is C or N. Similar as for LIBs', appropriately designed carbons are perhaps the most economical and technically viable candidate for NIB applications. A range of hard (“hard” is defined as non-graphitizable) carbons has been employed, including N-doped carbons. Recently, soft carbons have also been employed with good success.
Another commercially important energy storage system is an electrochemical capacitor, a.k.a. a supercapacitor, which provides greater power density and longer cycling life than a secondary battery, but at the expense of substantially decreased energy density. The main development target for supercapacitors is to expand their energy density without sacrificing too significantly their high power and high cyclability. A popular approach for achieving such balance is to design a device with a capacitor-type positive electrode (cathode) and battery-type negative electrode (anode). In such a system, termed a hybrid ion capacitor among other names, charge is stored by bulk ion insertion into the anode, similar as in a standard battery. However the positive electrode stores charge primarily by reversible ion adsorption rather than ion intercalation, aiding the rate capability and reducing cycling-induced degradation.
While there have been a great variety hybrid lithium and sodium ion capacitor architectures, they have generally relied on dissimilar materials in the cathode versus the anode. An aim of the present invention is a symmetric electrode architecture which employs similar or same materials in the cathode versus the anode.
Another aim in both battery and supercapacitor fields is to design high performance electrodes through green methods and from sustainable precursors, such as those derived from waste streams.